The plan of the proposed research derives from a model of the development of emotion, in which it is proposed that components of fear develop independently in the second half-year of life to form, only later, a complete "fear constellation". The study will examine the developmental histories of avoidance, expressive, and autonomic responses and their relationship to cognitive growth. Specifically, we will measure a motoric response, facial expressions and vocalizations, and heart rate in three "fearful" situations: the visual cliff, stranger approach, and looming. To assess the relationship of fear responses in these three situations to cognitive and visual development, infants will also be tested on a stage-four object permanence task, the Catford Test of Visual Acuity, and the Revised Gesell and Amatruda Developmental and Neurological Exam. The proposed study is longitudinal in design, in response to warning of the inappropriateness of cross-sectional designs for infant research in emotional development. Infants will be tested at 7, 8.5, 10, and 11.5 months of age. A group of normal infants and a group of Down's Syndrome infants will be tested. It is hoped that the study of Down's Syndrome infants will serve to clarify the relationship of cognition to the development of adaptive, expressive, and autonomic components of fear. We believe that the proposed research will provide critical data in the area of emotional development in infancy and its relationship to cognitive development and maturation. Further, we believe that the findings obtained could be used to help mothers of Down's Syndrome infants better understand their child's unique emotional and cognitive developmental patterns.